[phpmailer] Rework addon

- Remove redundant uninstall function
- Add default config file
- Add replyTo support
- Add custom headers support
- Add plain text-only support
- Improve error handling

phpmailer/config/phpmailer.config.php

@@ -0,0 +1,44 @@
+<?php
+
+// Warning: Don't change this file! It only holds the default config values for this addon.
+// Instead overwrite these config values in config/addon.config.php in your Friendica directory
+
+return [
+	'phpmailer' => [
+		// smtp (Boolean)
+		// Enables SMTP relaying for outbound emails
+		'smtp' => false,
+
+		// smtp_server (String)
+		// SMTP server host name
+		'smtp_server' => 'smtp.example.com',
+
+		// smtp_port (Integer)
+		// SMTP server port number
+		'smtp_port' => 25,
+
+		// smtp_secure (String)
+		// What kind of encryption to use on the SMTP connection.
+		// Options: '', 'ssl' or 'tls'.
+		'smtp_secure' => '',
+
+		// smtp_port_s (Integer)
+		// Secure SMTP server port number
+		'smtp_port_s' => 465,
+
+		// smtp_username (String)
+		// SMTP server authentication user name
+		// Empty string disables authentication
+		'smtp_username' => '',
+
+		// smtp_password (String)
+		// SMTP server authentication password
+		// Empty string disables authentication
+		'smtp_password' => '',
+
+		// smtp_from (String)
+		// From address used when using the SMTP server
+		// Example: no-reply@example.com
+		'smtp_from' => '',
+	],
+];